Photoflash lamp circuit



y 0, 1950 c. s. DAVIS 2,509,967

PHOTOFLASH LAMP CIRCUIT Filed June 9, 1947 k INVENTOR. F 73: 2- BYClinton Span/ s A z's At tor/veg.

Patented May 30, 1950 PHOTOFLASH LAMP CIRCUIT Clinton S. Davis, Chicago,Ill.

Application June 9, 1947, Serial No. 753,454

1 Claim.

This invention relates to certain new and useful improvements inphotoflash lamp circuits and has for its principal object the provisionof an improved construction which will be highly efflcient in use andeconomical in manufacture.

In photographing b the use of photographic flash lamps, it is a commonunderstanding that due to insufiicient illumination photographs do notresult in a well defined perspective and lack depth and detail largelybecause of this insuflicient illumination.

To overcome this objectionable feature it is a common practice to use amaster flash lamp to control a slave flash bulb, the latter usuallylocated where the photographer believes necessary for properillumination. In this employment of a master photographic flash lamp fordischarg ing a slave flash bulb, the discharge between the two should beas near simultaneous as it is possible to obtain. In most slave flashbulb circuits with which I am familiar, there is a measurable time lagbetween the master and the slave flash with the result that the finishedphotograph is defective due to the lack of proper illumination. It is,therefore, the object of this invention to provide a circuit for a slavephotographic flash bulb in which the flash of the slave bulb will beinstantaneous with the flash of the master flash lamp and wherein thetime lag between the master and slave flash is reduced to a minimum.

Other objects of the invention are the elimination of moving parts, suchas relays in the circuit; elimination of filament and filament supplycurrent; and a lower overall current drain.

Other objects will appear hereinafter.

The invention consists in the novel combination and arrangement of partsto be hereinafter described and claimed.

The invention will be best understood by reierence to the accompanyingdrawings showing the preferred form of construction, and in which:

Fig. 1 is a perspective view of a flash bulb stand having the slaveflash bulb control associated therewith; and

Fig. 2 is a circuit diagram for the slave photographic flash bulb.

The several objects of my invention are accom-- plished by the preferredform of construction shown in the accompanying drawings. In Fig. 1, Ihave fragmentarily illustrated a photographic slave flash bulb assembly.This assembly includes a stand supporting the reflector l l within whichis mounted the slave bulb 25. On this stand and mounted thereon in anysuitable manner is an enclosure l3 having an opening M to the rear ofwhich is arranged a photo-electric cell [5. The circuit of thisphoto-electric cell is connected to the slave flash bulb by a conductorit including the lines 24.

In Fig. 2 I have illustrated the circuit diagram. In this circuitdiagram the power source is indicated at H, and in this power source isa switch [8. This source could conveniently be a dry cell battery pack.

The circuit includes a voltage dividing potentiometer l9 and thephoto-electric cell l5. 2! is a glow discharge trigger-grid tube and inthis grid circuit is a trigger-grid current condenser 22.

An anode current limiting resistor is indicated at 23 and is in parallelwith the slave flash bulb 25. An anode voltage limiting resistor isindicated at 26 and includes an adjustment element 27. Between theresistors 23 and 26 and connected at one side to one of the powersources I! is an impulse storage condenser 28.

In the normal operation of my device, switch I8 is closed and thevoltage dividing potentiometer advanced to apply a potential such that adischarge takes place between the trigger-grid 2| and cathode.Sufflcient current flows to the trigger-grid current condenser 22 toassure that a breakdown occurs between the anode and the cathode. Thisanode-cathode discharge is unable to maintain itself due to the limitingaction of the anode voltage limiting resistor and so a pulsing conditionis established, its period being determined by the values of the anodevoltage limiting resistor and the impulse storage condenser. Thispulsing conditioning allows the trigger-gr'id 2i to retain control andif its potential is reduced the periodic cathode-anode discharge stops.Thus it becomes possible and practical-to utilize the trigger tube as anelectronic switch and at the same time as a visual indicating device,making it possible for the operator to make the proper circuitadjustment as described. Upon completion of such circuit adjustment thephoto-flash bulb 25 will be fired by the energy stored in the impulsestorage condenser 28 if there is an increase in the illumination fallingon the photo-electric cell I5 such as would occur if a masterphoto-flash bulb were fired so that its light fell on the photo-cell i5.The photo-flash bulb 25 requires a relatively high current on the orderof one ampere of very short duration for ignition. The charge stored inthe impulse condenser is capable upon release of causing a high currentsurge to pass through the igniter filament of the photo-flash bulb.

The characteristic steep front of this surge reduces substantially thetime normally required to initiate ignition in the slave photo-flashbulb. This advantage plus the almost instantaneous action of theelectronic circuit greatly reduces the lag between master and slaveflash over other arrangements in prior art.

A typical characteristic of grid controlled electronic discharge tubesis that of a substantial differential in grid potential existing betweenthat required to initiate discharge and that required to extinguish thisdischarge. In practice, this appears as back lash and precludes thepossibility, generally, of bringing the circuit to optimum sensitivity.In my invention, through the proper choice of competent values withspecial consideration to the internal resistance of the power source, itis possible to obtain an increase in grid potential immediately thedischarge is extinguished. This greatly reduces back lash and permitsoptimum sensitivity settings to be made with ease.

By the arrangement herein set forth it might be said that the slavecircuit has been primed for the flash discharge and that all thatremains is for the increase in the illumination upon the photo-cell I toeffect the instantaneous flash between the slave bulb and a master bulb.

While .I have illustrated and described the preferred form ofconstruction for carrying my invention into "efiect, this is capable ofvariation and modification without departing from the spirit of theinvention. I, therefore, do not wish to 'be limited to the precisedetails of construction set forth, but desire to avail myself of suchvariations and modifications as come within the scope of the appendedclaim.

Having thus described my invention, what I claim as new and desire toprotect by Letters Patent is:

In a slave photo-flash circuit comprising a power line having a controlswitch, a voltage dividing potentiometer across the power line whichincludes a variable arm, a glow discharge trigger grid tube with itscathode in circuit with one side of the power line and its grid incircuit with the variable arm of the potentiom eter, a trigger gridcondenser across said one side of the power line and said arm, aphoto-cell connected across the said arm and the other side of the powerline, an anode voltage limiting resistor which includes a variable arm,an anode current limiting resistor having one side in circuit with theplate of said tube and the other side thereof in circuit with the anodevoltage limiting resistor, a flash bulb connected across the anodecurrent limiting resistor, the variable arm ofsaid anode voltagelimiting resistor being connected to said other side of the power line,and an impulse storage condenser having one side in circuit with saidone side of the power line and the other side thereof in circuit withsaid one side of said anode voltage limiting resistor.

CLINTON S. DAVIS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,269,338 Ed'ger'ton -Jan. 6,1942 2,331,771 Germes'hausen et a1. Oct. 12, 1943 2,336,633 Parson Dec.14, 1943 2,411,531 Engelhar'dt 1 Nov. 26, 1946 2,432,084 Blair Dec. 9,1947

